Functionalized polymer, rubber composition and pneumatic tire

ABSTRACT

The present invention is directed to a functionalized elastomer comprising the reaction product of a living anionic elastomeric polymer and a polymerization terminator of formula I 
     
       
         
         
             
             
         
       
     
     wherein R 1  is C1 to C4 linear alkyl, or C1 to C4 branched alkanediyl; X 1 , X 2 , X 3  are independently O, S, or a group of formula (II) or (III) 
     
       
         
         
             
             
         
       
     
     where R 2  is C1 to C18 linear or branched alkyl; and Z is —R 3 —CH═CH—R 4 , where R 3  is a covalent bond or C1 to C18 linear or branched alkanediyl, and R 4  is a hydrogen or C1 to C18 linear or branched alkyl.

BACKGROUND OF THE INVENTION

In recent years, there is a growing demand for functionalized polymers. Functionalized polymers can be synthesized through various living/controlled polymerization techniques. In the living polymerization process, based on an active carbanionic center, metals from Groups I and II of the periodic table are commonly used to initiate the polymerization of monomers into polymers. For example, lithium, barium, magnesium, sodium, and potassium are metals that are frequently utilized in such polymerizations. Initiator systems of this type are of commercial importance because they can be used to produce stereoregulated polymers. For instance, lithium initiators can be utilized to initiate the anionic polymerization of isoprene into synthetic polyisoprene rubber or to initiate the polymerization of 1,3-butadiene into polybutadiene rubber having the desired microstructure.

The polymers formed in such polymerizations have the metal used to initiate the polymerization at the growing end of their polymer chains and are sometimes referred to as living polymers. They are referred to as living polymers because their polymer chains, which contain the terminal metal initiator, continue to grow or live until all of the available monomer is exhausted. Polymers that are prepared by utilizing such metal initiators normally have structures which are essentially linear and normally do not contain appreciable amounts of branching.

This invention details the synthesis of functionalized polymers and their use in rubber formulation and tire materials. Often, to achieve the best tire performance properties, functionalized polymers are highly desirable. In order to reduce the rolling resistance and to improve the tread wear characteristics of tires, functionalized elastomers having a high rebound physical property (low hysteresis) have been used for the tire tread rubber compositions. However, in order to increase the wet skid resistance of a tire tread, rubbery polymers that have a relatively lower rebound physical property (higher hysteresis) which thereby undergo a greater energy loss, have sometimes been used for such tread rubber compositions. To achieve these desired viscoelastic properties for the tire tread rubber compositions, blends (mixtures) of various types of synthetic and natural rubber can be utilized in tire treads.

Functionalized rubbery polymers made by living polymerization techniques are typically compounded with sulfur, accelerators, antidegradants, a filler (such as carbon black, silica or starch) and other desired rubber chemicals. These are then subsequently vulcanized or cured into the form of a useful article, such as a tire or a power transmission belt. It has been established that many physical properties of such cured rubbers depend upon the degree to which the filler is homogeneously dispersed throughout the rubber. This is, in turn, related to the level of affinity that filler has for the particular rubbery polymer. This can be of practical importance in improving the physical characteristics of rubber articles which are made utilizing such rubber compositions. For example, the rolling resistance and traction characteristics of tires can be improved by improving the affinity of carbon black and/or silica to the rubbery polymer utilized therein. Therefore, it would be highly desirable to improve the affinity of a given rubbery polymer for fillers, such as carbon black and silica.

In tire tread formulations, better interaction between the filler and the rubbery polymer results in lower hysteresis and consequently tires made with such rubber formulations have lower rolling resistance. Low tan delta values at 60° C. are indicative of low hysteresis and consequently tires made utilizing such rubber formulations with low tan delta values at 60° C. normally exhibit lower rolling resistance. Better interaction between the filler and the rubbery polymer in tire tread formulations also typically results in higher tan delta values at 0° C. which is indicative of better traction characteristics.

The interaction between rubber and carbon black has been attributed to a combination of physical absorption (van der Waals force) and chemisorption between the oxygen containing functional groups on the carbon black surface and the rubber (see D. Rivin, J. Aron, and A. Medalia, Rubber Chemical & Technology 41, 330 (1968) and A. Gessler, W. Hess, and A Medalia, Plastic Rubber Process, 3, 141 (1968)). Various other chemical modification techniques, especially for styrene-butadiene rubber made by solution polymerization (S-SBR), have also been described for reducing hysteresis loss by improving polymer-filler interactions. In one of these techniques, the solution rubber chain end is modified with aminobenzophenone. This greatly improves the interaction between the polymer and the oxygen-containing groups on the carbon black surface (see N. Nagata, Nippon Gomu Kvokaishi, 62, 630 (1989)). Tin coupling of anionic solution polymers is another commonly used chain end modification method that aids polymer-filler interaction supposedly through increased reaction with the quinone groups on the carbon black surface. The effect of this interaction is to reduce the aggregation between carbon black particles which in turn, improves dispersion and ultimately reduces hysteresis.

SUMMARY OF THE INVENTION

The subject invention provides a low cost means for the end-group functionalization of rubbery living polymers to improve their affinity for fillers, such as carbon black and/or silica. Such functionalized polymers can be beneficially used in manufacturing tires and other rubber products where improved polymer/filler interaction is desirable. In tire tread compounds this can result in lower polymer hysteresis which in turn can provide a lower level of tire rolling resistance.

The present invention is directed to a functionalized elastomer comprising the reaction product of a living anionic elastomeric polymer and a polymerization terminator of formula I

wherein R¹ is C1 to C4 linear alkanediyl, or C1 to C4 branched alkanediyl; X¹, X², X³ are independently O, S, or a group of formula (II) or (III)

where R² is C1 to C18 linear or branched alkyl; and Z is —R³—CH═CH—R⁴, where R³ is a covalent bond or C1 to C18 linear or branched alkane diyl, and R⁴ is a hydrogen or C1 to C18 linear or branched alkyl.

The invention is further directed to a rubber composition comprising the functionalized elastomer, and a pneumatic tire comprising the rubber composition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a graph of torque versus cure time for several rubber samples.

FIG. 2 shows a graph of G′ versus percent strain for several rubber samples.

FIG. 3 shows a graph of tan delta versus percent strain for several rubber samples.

DETAILED DESCRIPTION OF THE INVENTION

There is disclosed a functionalized elastomer comprising the reaction product of a living anionic elastomeric polymer and a polymerization terminator of formula I

wherein R¹ is C1 to C4 linear alkyl, or C1 to C4 branched alkanediyl; X¹, X², X³ are independently O, S, or a group of formula (II) or (III)

where R² is C1 to C18 linear or branched alkyl; and Z is —R³—CH═CH—R₄, where R³ is a covalent bond or C1 to C18 linear or branched alkane diyl, and R⁴ is a hydrogen or C1 to C18 linear or branched alkyl.

There is further disclosed a rubber composition comprising the functionalized elastomer, and a pneumatic tire comprising the rubber composition.

The subject invention provides a means for the end-group functionalization of rubbery living polymers to improve their affinity for fillers, such as carbon black and/or silica. The process of the present invention can be used to functionalize any living polymer which is terminated with a metal of group I or II of the periodic table. These polymers can be produced utilizing techniques that are well known to persons skilled in the art. The metal terminated rubbery polymers that can be functionalized with a terminator of formula I in accordance with this invention can be made utilizing monofunctional initiators resulting in polymers having the general structural formula P-M, wherein P represents a polymer chain and wherein M represents a metal of group I or II. The metal initiators utilized in the synthesis of such metal terminated polymers can also be multifunctional organometallic compounds. For instance, difunctional organometallic compounds can be utilized to initiate such polymerizations. The utilization of such difunctional organometallic compounds as initiators generally results in the formation of polymers having the general structural formula M-P-M, wherein P represents a polymer chain and wherein M represents a metal of group I or II. Such polymers, which are terminated at both of their chain ends with a metal from group I or II, also can be reacted with terminator of formula I to functionalize both of their chain ends. It is believed that utilizing difunctional initiators so that both ends of the polymers chain can be functionalized with the terminator of formula I can further improve interaction with fillers, such as carbon black and silica.

The initiator used to initiate the polymerization employed in synthesizing the living rubbery polymer that is functionalized in accordance with this invention is typically selected from the group consisting of barium, lithium, magnesium, sodium, and potassium. Reagents consisting of barium, lithium, magnesium, sodium, and potassium alkyls may also be used. Lithium and magnesium are the metals that are most commonly utilized in the synthesis of such metal terminated polymers (living polymers). Normally, alkyllithium initiators are more preferred.

Organolithium compounds are the preferred initiators for utilization in such polymerizations. The organolithium compounds which are utilized as initiators are normally organo monolithium compounds. The organolithium compounds which are preferred as initiators are monofunctional compounds which can be represented by the formula: R—Li, wherein R represents a hydrocarbyl radical containing from 1 to about 20 carbon atoms. Generally, such monofunctional organolithium compounds will contain from 1 to about 10 carbon atoms. Some representative examples of preferred reagents are butyllithium, secbutyllithium, n-hexyllithium, n-octyllithium, tertoctyllithium, n-decyllithium, phenyllithium, 1-naphthyllithium, 4-butylphenyllithium, p-tolyllithium, 4-phenylbutyllithium, cyclohexyllithium, 4-butylcyclohexyllithium, and 4-cyclohexylbutyllithium. Secondary butyllithium is a highly preferred organolithium initiator. Very finely divided lithium having an average particle diameter of less than 2 microns can also be employed as the initiator for the synthesis of living rubbery polymers that can be functionalized with a terminator of formula I in accordance with this invention. U.S. Pat. No. 4,048,420, which is incorporated herein by reference in its entirety, describes the synthesis of lithium terminated living polymers utilizing finely divided lithium as the initiator. Lithium amides can also be used as the initiator in the synthesis of living polydiene rubbers (see U.S. Pat. No. 4,935,471, the teaching of which are incorporated herein by reference with respect to lithium amides that can be used as initiators in the synthesis of living rubbery polymer).

The amount of organolithium initiator utilized will vary depending upon the molecular weight which is desired for the rubbery polymer being synthesized as well as the precise polymerization temperature which will be employed. The precise amount of organolithium compound required to produce a polymer of a desired molecular weight can be easily ascertained by persons skilled in the art. However, as a general rule from 0.01 to 1 phm (parts per 100 parts by weight of monomer) of an organolithium initiator will be utilized. In most cases, from 0.01 to 0.1 phm of an organolithium initiator will be utilized with it being preferred to utilize 0.025 to 0.07 phm of the organolithium initiator.

Many types of unsaturated monomers which contain carbon-carbon double bonds can be polymerized into polymers using such metal catalysts. Elastomeric or rubbery polymers can be synthesized by polymerizing diene monomers utilizing this type of metal initiator system. The diene monomers that can be polymerized into synthetic rubbery polymers can be either conjugated or non-conjugated diolefins. Conjugated diolefin monomers containing from 4 to 8 carbon atoms are generally preferred. Vinyl-substituted aromatic monomers can also be copolymerized with one or more diene monomers into rubbery polymers, for example styrene-butadiene rubber (SBR). Some representative examples of conjugated diene monomers that can be polymerized into rubbery polymers include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, 2-methyl 1,3-pentadiene, 2,3-dimethyl-1,3-pentadiene, 2-phenyl-1,3-butadiene, and 4,5-diethyl-1,3-octadiene. Some representative examples of vinyl-substituted aromatic monomers that can be utilized in the synthesis of rubbery polymers include styrene, 1-vinylnapthalene, 3-methylstyrene, 3,5-diethylstyrene, 4-propylstyrene, 2,4,6-trimethylstyrene, 4-dodecylstyrene, 3-methyl-5-normal-hexylstyrene, 4-phenylstyrene, 2-ethyl-4-benzylstyrene, 3,5-diphenylstyrene, 2,3,4,5-tetraethylstyrene, 3-ethyl-1-vinylnapthalene, 6-isopropyl-1-vinylnapthalene, 6-cyclohexyl-1-vinylnapthalene, 7-dodecyl-2-vinylnapthalene, o-methylstyrene, and the like.

The metal terminated rubbery polymers that are functionalized with a terminator of formula I in accordance with this invention are generally prepared by solution polymerizations that utilize inert organic solvents, such as saturated aliphatic hydrocarbons, aromatic hydrocarbons, or ethers. The solvents used in such solution polymerizations will normally contain from about 4 to about 10 carbon atoms per molecule and will be liquids under the conditions of the polymerization. Some representative examples of suitable organic solvents include pentane, isooctane, cyclohexane, normal-hexane, benzene, toluene, xylene, ethylbenzene, tetrahydrofuran, and the like, alone or in a mixture. For instance, the solvent can be a mixture of different hexane isomers. Such solution polymerizations result in the formation of a polymer cement (a highly viscous solution of the polymer).

The metal terminated living rubbery polymers utilized in the practice of this invention can be of virtually any molecular weight. However, the number average molecular weight of the living rubbery polymer will typically be within the range of about 50,000 to about 500,000. It is more typical for such living rubbery polymers to have number average molecular weights within the range of 100,000 to 250,000.

The metal terminated living rubbery polymer can be functionalized by simply adding a stoichiometric amount of a terminator of formula I to a solution of the rubbery polymer (a rubber cement of the living polymer). In other words, approximately one mole of the terminator of formula I is added per mole of terminal metal groups in the living rubbery polymer. The number of moles of metal end groups in such polymers is assumed to be the number of moles of the metal utilized in the initiator. It is, of course, possible to add greater than a stoichiometric amount of the terminator of formula I. However, the utilization of greater amounts is not beneficial to final polymer properties. Nevertheless, in many cases it will be desirable to utilize a slight excess of the terminator of formula I to ensure that at least a stoichiometric amount is actually employed or to control the stoichiometry of the functionalization reaction. In most cases from about 0.8 to about 1.1 moles of the terminator of formula I will be utilized per mole of metal end groups in the living polymer being treated. In the event that it is not desired to functionalize all of the metal terminated chain ends in a rubbery polymer then, of course, lesser amounts of the terminator of formula I can be utilized.

The terminator of formula I will react with the metal terminated living rubbery polymer over a very wide temperature range. For practical reasons, the functionalization of such living rubbery polymers will normally be carried out at a temperature within the range of 0° C. to 150° C. In order to increase reaction rates, in most cases it will be preferred to utilize a temperature within the range of 20° C. to 100° C. with temperatures within the range of 50° C. to 80° C. being most preferred. The capping reaction is very rapid and only very short reaction times within the range of 0.5 to 4 hours are normally required. However, in some cases reaction times of up to about 24 hours may be employed.

After the functionalization reaction is completed, it will normally be desirable to quench any living chains which remain. This can be accomplished by adding an alcohol, such as methanol or ethanol, to the polymer cement after the functionalization reaction is completed in order to eliminate any living polymer that was not consumed by the reaction with the terminator of formula I. The end-group functionalized polydiene rubber can then be recovered from the solution utilizing standard techniques.

The functionalized polymer may be compounded into a rubber composition. The rubber composition may optionally include, in addition to the functionalized polymer, one or more rubbers or elastomers containing olefinic unsaturation. The phrases “rubber” or “elastomer containing olefinic unsaturation” or “diene-based elastomer” are intended to include both natural rubber and its various raw and reclaim forms as well as various synthetic rubbers. In the description of this invention, the terms “rubber” and “elastomer” may be used interchangeably, unless otherwise prescribed. The terms “rubber composition,” “compounded rubber” and “rubber compound” are used interchangeably to refer to rubber which has been blended or mixed with various ingredients and materials and such terms are well known to those having skill in the rubber mixing or rubber compounding art. Representative synthetic polymers are the homopolymerization products of butadiene and its homologues and derivatives, for example, methylbutadiene, dimethylbutadiene and pentadiene as well as copolymers such as those formed from butadiene or its homologues or derivatives with other unsaturated monomers. Among the latter are acetylenes, for example, vinyl acetylene; olefins, for example, isobutylene, which copolymerizes with isoprene to form butyl rubber; vinyl compounds, for example, acrylic acid, acrylonitrile, which polymerize with butadiene to form NBR, methacrylic acid and styrene, the latter compound polymerizing with butadiene to form SBR, as well as vinyl esters and various unsaturated aldehydes, ketones and ethers, e.g., acrolein, methyl isopropenyl ketone and vinylethyl ether. Specific examples of synthetic rubbers include neoprene (polychloroprene), polybutadiene (including cis-1,4-polybutadiene), polyisoprene (including cis-1,4polyisoprene), butyl rubber, halobutyl rubber such as chlorobutyl rubber or bromobutyl rubber, styrene/isoprene/butadiene rubber, copolymers of 1,3-butadiene or isoprene with monomers such as styrene, acrylonitrile and methyl methacrylate, as well as ethylene/propylene terpolymers, also known as ethylene/propylene/diene monomer (EPDM), and in particular, ethylene/propylene/dicyclopentadiene terpolymers. Additional examples of rubbers which may be used include alkoxy-silyl end functionalized solution polymerized polymers (SBR, PBR, IBR and SIBR), silicon-coupled and tin-coupled star-branched polymers. The preferred rubber or elastomers are polyisoprene (natural or synthetic), polybutadiene and SBR.

In one aspect, the at least one additional rubber is preferably of at least two of diene based rubbers. For example, a combination of two or more rubbers is preferred such as cis 1,4-polyisoprene rubber (natural or synthetic, although natural is preferred), 3,4-polyisoprene rubber, styrene/isoprene/butadiene rubber, emulsion and solution polymerization derived styrene/butadiene rubbers, cis 1,4-polybutadiene rubbers and emulsion polymerization prepared butadiene/acrylonitrile copolymers.

In one aspect of this invention, an emulsion polymerization derived styrene/butadiene (E-SBR) might be used having a relatively conventional styrene content of about 20 to about 28 percent bound styrene or, for some applications, an E-SBR having a medium to relatively high bound styrene content, namely, a bound styrene content of about 30 to about 45 percent.

By emulsion polymerization prepared E-SBR, it is meant that styrene and 1,3-butadiene are copolymerized as an aqueous emulsion. Such are well known to those skilled in such art. The bound styrene content can vary, for example, from about 5 to about 50 percent. In one aspect, the E-SBR may also contain acrylonitrile to form a terpolymer rubber, as E-SBAR, in amounts, for example, of about 2 to about 30 weight percent bound acrylonitrile in the terpolymer.

Emulsion polymerization prepared styrene/butadiene/acrylonitrile copolymer rubbers containing about 2 to about 40 weight percent bound acrylonitrile in the copolymer are also contemplated as diene based rubbers for use in this invention.

The solution polymerization prepared SBR (S-SBR) typically has a bound styrene content in a range of about 5 to about 50, preferably about 9 to about 36, percent. The S-SBR can be conveniently prepared, for example, by organo lithium catalyzation in the presence of an organic hydrocarbon solvent.

In one embodiment, cis 1,4-polybutadiene rubber (BR) may be used. Such BR can be prepared, for example, by organic solution polymerization of 1,3-butadiene. The BR may be conveniently characterized, for example, by having at least a 90 percent cis 1,4-content.

The cis 1,4-polyisoprene and cis 1,4-polyisoprene natural rubber are well known to those having skill in the rubber art.

The term “phr” as used herein, and according to conventional practice, refers to “parts by weight of a respective material per 100 parts by weight of rubber, or elastomer.”

The rubber composition may also include up to 70 phr of processing oil. Processing oil may be included in the rubber composition as extending oil typically used to extend elastomers. Processing oil may also be included in the rubber composition by addition of the oil directly during rubber compounding. The processing oil used may include both extending oil present in the elastomers, and process oil added during compounding. Suitable process oils include various oils as are known in the art, including aromatic, paraffinic, naphthenic, vegetable oils, and low PCA oils, such as MES, TDAE, SRAE and heavy naphthenic oils. Suitable low PCA oils include those having a polycyclic aromatic content of less than 3 percent by weight as determined by the IP346 method. Procedures for the IP346 method may be found in Standard Methods for Analysis & Testing of Petroleum and Related Products and British Standard 2000 Parts, 2003, 62nd edition, published by the Institute of Petroleum, United Kingdom.

The rubber composition may include from about 10 to about 150 phr of silica. In another embodiment, from 20 to 80 phr of silica may be used.

The commonly employed siliceous pigments which may be used in the rubber compound include conventional pyrogenic and precipitated siliceous pigments (silica). In one embodiment, precipitated silica is used. The conventional siliceous pigments employed in this invention are precipitated silicas such as, for example, those obtained by the acidification of a soluble silicate, e.g., sodium silicate.

Such conventional silicas might be characterized, for example, by having a BET surface area, as measured using nitrogen gas. In one embodiment, the BET surface area may be in the range of about 40 to about 600 square meters per gram. In another embodiment, the BET surface area may be in a range of about 80 to about 300 square meters per gram. The BET method of measuring surface area is described in the Journal of the American Chemical Society, Volume 60, Page 304 (1930).

The conventional silica may also be characterized by having a dibutylphthalate (DBP) absorption value in a range of about 100 to about 400, alternatively about 150 to about 300.

The conventional silica might be expected to have an average ultimate particle size, for example, in the range of 0.01 to 0.05 micron as determined by the electron microscope, although the silica particles may be even smaller, or possibly larger, in size.

Various commercially available silicas may be used, such as, only for example herein and without limitation, silicas commercially available from PPG Industries under the Hi-Sil trademark with designations 210, 243, etc; silicas available from Rhodia, with, for example, designations of Z1165MP and Z165GR and silicas available from Degussa AG with, for example, designations VN2 and VN3, etc.

Commonly employed carbon blacks can be used as a conventional filler in an amount ranging from 10 to 150 phr. In another embodiment, from 20 to 80 phr of carbon black may be used. Representative examples of such carbon blacks include N110, N121, N134, N220, N231, N234, N242, N293, N299, N315, N326, N330, N332, N339, N343, N347, N351, N358, N375, N539, N550, N582, N630, N642, N650, N683, N754, N762, N765, N774, N787, N907, N908, N990 and N991. These carbon blacks have iodine absorptions ranging from 9 to 145 g/kg and DBP number ranging from 34 to 150 cm³/100 g.

Other fillers may be used in the rubber composition including, but not limited to, particulate fillers including ultra high molecular weight polyethylene (UHMWPE), crosslinked particulate polymer gels including, but not limited to, those disclosed in U.S. Pat. Nos. 6,242,534; 6,207,757; 6,133,364; 6,372,857; 5,395,891; or 6,127,488, and plasticized starch composite filler including but not limited to that disclosed in U.S. Pat. No. 5,672,639. Such other fillers may be used in an amount ranging from 1 to 30 phr.

In one embodiment, the rubber composition may contain a conventional sulfur containing organosilicon compound. In one embodiment, the sulfur containing organosilicon compounds are 3,3′-bis(trimethoxy or triethoxy silylpropyl) polysulfides. In one embodiment, the sulfur containing organosilicon compounds are 3,3′-bis(triethoxysilylpropyl) disulfide and/or 3,3′-bis(triethoxysilylpropyl) tetrasulfide.

In another embodiment, suitable sulfur containing organosilicon compounds include compounds disclosed in U.S. Pat. No. 6,608,125. In one embodiment, the sulfur containing organosilicon compounds includes 3-(octanoylthio)-1-propyltriethoxysilane, CH₃(CH₂)₆C(═O)—S—CH₂CH₂CH₂Si(OCH₂CH₃)₃, which is available commercially as NXT™ from Momentive Performance Materials.

In another embodiment, suitable sulfur containing organosilicon compounds include those disclosed in U.S. Patent Publication No. 2003/0130535. In one embodiment, the sulfur containing organosilicon compound is Si-363 from Degussa.

The amount of the sulfur containing organosilicon compound in a rubber composition will vary depending on the level of other additives that are used. Generally speaking, the amount of the compound will range from 0.5 to 20 phr. In one embodiment, the amount will range from 1 to 10 phr.

It is readily understood by those having skill in the art that the rubber composition would be compounded by methods generally known in the rubber compounding art, such as mixing the various sulfur-vulcanizable constituent rubbers with various commonly used additive materials such as, for example, sulfur donors, curing aids, such as activators and retarders and processing additives, such as oils, resins including tackifying resins and plasticizers, fillers, pigments, fatty acid, zinc oxide, waxes, antioxidants and antiozonants and peptizing agents. As known to those skilled in the art, depending on the intended use of the sulfur vulcanizable and sulfur-vulcanized material (rubbers), the additives mentioned above are selected and commonly used in conventional amounts. Representative examples of sulfur donors include elemental sulfur (free sulfur), an amine disulfide, polymeric polysulfide and sulfur olefin adducts. In one embodiment, the sulfur-vulcanizing agent is elemental sulfur. The sulfur-vulcanizing agent may be used in an amount ranging from 0.5 to 8 phr, alternatively with a range of from 1.5 to 6 phr. Typical amounts of tackifier resins, if used, comprise about 0.5 to about 10 phr, usually about 1 to about 5 phr. Typical amounts of processing aids comprise about 1 to about 50 phr. Typical amounts of antioxidants comprise about 1 to about 5 phr. Representative antioxidants may be, for example, diphenyl-p-phenylenediamine and others, such as, for example, those disclosed in The Vanderbilt Rubber Handbook (1978), Pages 344 through 346. Typical amounts of antiozonants comprise about 1 to 5 phr. Typical amounts of fatty acids, if used, which can include stearic acid comprise about 0.5 to about 3 phr. Typical amounts of zinc oxide comprise about 2 to about 5 phr. Typical amounts of waxes comprise about 1 to about 5 phr. Often microcrystalline waxes are used. Typical amounts of peptizers comprise about 0.1 to about 1 phr. Typical peptizers may be, for example, pentachlorothiophenol and dibenzamidodiphenyl disulfide.

Accelerators are used to control the time and/or temperature required for vulcanization and to improve the properties of the resulting vulcanizate. In one embodiment, a single accelerator system may be used, i.e., primary accelerator. The primary accelerator(s) may be used in total amounts ranging from about 0.5 to about 4, alternatively about 0.8 to about 1.5, phr. In another embodiment, combinations of a primary and a secondary accelerator might be used with the secondary accelerator being used in smaller amounts, such as from about 0.05 to about 3 phr, in order to activate and to improve the properties of the vulcanizate. Combinations of these accelerators might be expected to produce a synergistic effect on the final properties and are somewhat better than those produced by use of either accelerator alone. In addition, delayed action accelerators may be used which are not affected by normal processing temperatures but produce a satisfactory cure at ordinary vulcanization temperatures. Vulcanization retarders might also be used. Suitable types of accelerators that may be used in the present invention are amines, disulfides, guanidines, thioureas, thiazoles, thiurams, sulfenamides, dithiocarbamates and xanthates. In one embodiment, the primary accelerator is a sulfenamide. If a second accelerator is used, the secondary accelerator may be a guanidine, dithiocarbamate or thiuram compound.

The mixing of the rubber composition can be accomplished by methods known to those having skill in the rubber mixing art. For example, the ingredients are typically mixed in at least two stages, namely, at least one non-productive stage followed by a productive mix stage. The final curatives including sulfur-vulcanizing agents are typically mixed in the final stage which is conventionally called the “productive” mix stage in which the mixing typically occurs at a temperature, or ultimate temperature, lower than the mix temperature(s) than the preceding non-productive mix stage(s). The terms “non-productive” and “productive” mix stages are well known to those having skill in the rubber mixing art. The rubber composition may be subjected to a thermomechanical mixing step. The thermomechanical mixing step generally comprises a mechanical working in a mixer or extruder for a period of time suitable in order to produce a rubber temperature between 140° C. and 190° C. The appropriate duration of the thermomechanical working varies as a function of the operating conditions, and the volume and nature of the components. For example, the thermomechanical working may be from 1 to 20 minutes.

The rubber composition may be incorporated in a variety of rubber components of the tire. For example, the rubber component may be a tread (including tread cap and tread base), sidewall, apex, chafer, sidewall insert, wirecoat or innerliner. In one embodiment, the component is a tread.

The pneumatic tire of the present invention may be a race tire, passenger tire, aircraft tire, agricultural, earthmover, off-the-road, truck tire, and the like. In one embodiment, the tire is a passenger or truck tire. The tire may also be a radial or bias.

Vulcanization of the pneumatic tire of the present invention is generally carried out at conventional temperatures ranging from about 100° C. to 200° C. In one embodiment, the vulcanization is conducted at temperatures ranging from about 110° C. to 180° C. Any of the usual vulcanization processes may be used such as heating in a press or mold, heating with superheated steam or hot air. Such tires can be built, shaped, molded and cured by various methods which are known and will be readily apparent to those having skill in such art.

This invention is illustrated by the following examples that are merely for the purpose of illustration and are not to be regarded as limiting the scope of the invention or the manner in which it can be practiced. Unless specifically indicated otherwise, parts and percentages are given by weight.

Example 1

Trisopropanolamine (TIPA, 1.00 eq, from Aldrich), vinyltriethoxysilane (V-TEOS, 1.02 eq, from Aldrich) and sodium hydroxide (2 percent, from Aldrich) were mixed in a 1-liter 3-neck round bottom flask equipped with vacuum distillation apparatus. Over a four-hour period, the mixture was heated from 30 to 60° C. and ethanol produced from the reaction was removed under reduced pressure of 200 to 20 mm Hg. The crude solid was then recrystallized from hexanes. Drying under vacuum gave 201.2 g (87 percent yield) of the purified 1-vinyl-3,7,10-trimethylsilatrane (VPOS) as a white crystalline solid. ¹H-NMR and ¹³C-NMR spectroscopy analysis has shown larger than 95 percent purity of the desired product. Melting Point: 98-101° C.

Example 2

In this example, bench scale synthesis of a functionalized elastomer is illustrated. Polymerizations were performed in a 1-quart bottle and heated by means of a 65° C. water bath. Monomer premix of styrene and butadiene (360.5 g, 15 wt percent) was charged into reactor with hexane as solvent followed by addition of modifier (TMEDA, 0.185 mL) and initiator (n-butyllithium, 0.31 mL, 1.45 mol/L). When the conversion was above 98 percent (2 hours), the polymerizations were terminated with functional terminators of Example 1. Hexane was evaporated by dropping polymer cement into hot water. Sample was dried in air for one day and then in 70° C. oven for 2 hours.

The polymers obtained were characterized using different techniques, for example, size exclusion chromatography (SEC) for determination of molecular weight, dynamic scanning calorimetry (DSC) for determination of T_(g), IR for determining cis, trans, styrene and vinyl content, and Mooney viscosity measurements with results given in Tables 1 and 2.

TABLE 1 Polymer Sample Overall Mn (kg/mol) PDI Sulfanylsilane-SBR¹ (comparative) 206 1.29 SBR² (control) 181 1.04 VPOS-SBR-A³ 255 1.51 VPOS-SBR-B⁴ 261 1.48 ¹Sulfanylsilane functionalized solution polymerized styrene-butadiene rubber, available commercially as Sprintan ® SLR 4602, from Styron ²Solution polymerized styrene-butadiene rubber terminated using isopropanol ³Solution polymerized styrene-butadiene terminated with 0.5 eq terminator of Example 1 ⁴Solution polymerized styrene-butadiene terminated with 0.75 eq terminator of Example 1

TABLE 2 Tg Polymer Inflection, Sample Mooney Cis Trans Styrene Vinyl¹ ° C. SBR-1: 67 15 15 20 50 −22 Sulfanylsilane- SBR (compar- ative) SBR-2: Non- 65 16 15 20 49 −21 functionalized SBR (control) SBR-3: VPOS- 62 16 14 20 51 −21 SBR-A SBR-4: VPOS- 58 15 15 20 52 −21 SBR-B ¹Vinyl content expressed as weight percent based on total polymer weight

Example 3

The VPOS-functionalized SBR copolymers of Example 2 (SBR-3 and SBR-4) as well as control (SBR-2) and a comparative sulfanylsilane functionalized SBR (SBR-1) were subsequently compounded.

Rubber compounds were mixed in a 3-piece 75 mL CW Brabender® mixer equipped with Banbury® rotor. Each SBR sample was mixed with additives in a two-stage mix procedure as shown in Table 3, with all amounts given in parts by weight, per 100 parts by weight of elastomer (phr). In the non-productive mix stage, compounds were mixed for 4 minutes at 100 rpm using 120° C. as starting temperature. Productive mixes were carried out at an 80° C. starting temperature and 60 rpm with mix time of 3 minute.

The compounds were tested for rheology properties using an RPA 2000® from Alpha Technology. Productive compounds were first heated to 100° C. and the storage modulus was measured at a frequency of 0.83 Hz and 15 percent strain in order to determine the processability of the compounds. Subsequently the compounds were cured at 160° C. for 16 minutes at the lowest possible strain (0.7 percent) to mimic a static cure. Then the compounds were cooled to 100° C., and a subsequent strain sweep is performed. Results are shown in Table 4 and FIGS. 1 to 3.

TABLE 3 SBR 100 Silica 65 Silane coupling agent 5.2 Stearic acid 2 Oil 20 Antidegradants 2.75 Waxes 1.5 Sulfur 1.7 Accelerators 3.1

TABLE 4 Sample No. SBR-1 SBR-2 SBR-3 SBR-4 Uncured G′ at 0.83 Hz (kPa) 321 259 312 319 G′ 1% (kPa) 3873 5637 3767 3614 Tan delta 10% 0.088 0.11 0.1 0.092 300% M (MPa) 9.35 7.62 8.9 9.08 Tensile strain at Max (%) 446 493 454 483 300/100 modulus 4.14 3.39 3.8 3.83

As seen in FIG. 1, MDR curves show that samples were vulcanized in a similar rate, which indicates that the silatrane functional groups of the polymer (SBR-3 and SBR-4) do not notably interfere with the vulcanization process compared to non-functionalized control.

The storage modulus, RPA G′ curves in FIG. 2 indicate an increase in polymer filler interaction for samples containing silatrane functional groups (SBR-3 and SBR-4), compared to non-functionalized control, SBR-2. Such increased polymer filler interaction is shown as reduced Payne effect. The Payne effect is the nonlinear dynamic mechanical property of elastomers in the presence of filler first studied by Payne, Appl. Polym. Sci., 6, 57 (1962). Generally it is associated with the breakdown and agglomeration of filler particles. In the presence of functionalized elastomer, the interaction of polar functional groups and filler particles, e.g. silica, facilitates the filler network breakdown, which may lead to better filler dispersion. Tan delta curves (FIG. 3) have shown lower values for samples containing functionalized polymer disclosed herein (SBR-3 and SBR-4), compared to non-functionalized control, SBR-2. Lower tan delta may also indicate better polymer filler interaction, as well as better silica dispersion.

While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention. 

What is claimed is:
 1. A functionalized elastomer comprising the reaction product of a living anionic elastomeric polymer and a polymerization terminator of formula I

wherein R¹ is C1 to C4 linear alkanediyl, or C1 to C4 branched alkanediyl; X¹, X², X³ in formula I may be independently O, S, a group of formula II, or a group of formula III;

where R² is C1 to C18 linear or branched alkyl; and Z is —R³— CH═CH—R⁴, where R³ is a covalent bond or C1 to C18 linear or branched alkanediyl, and R⁴ is a hydrogen or C1 to C18 linear or branched alkyl.
 2. The functionalized elastomer of claim 1, wherein the living anionic elastomer is derived from at least one diene monomer and optionally at least one vinyl aromatic monomer.
 3. The functionalized elastomer of claim 1, wherein the living anionic elastomer is derived from at least one of isoprene and butadiene, and optionally from styrene.
 4. The functionalized elastomer of claim 1, wherein the living anionic elastomer is derived from butadiene and styrene.
 5. The functionalized elastomer of claim 1, wherein the polymerization terminator of formula I is of the following structure


6. A rubber composition comprising the functionalized elastomer of claim
 1. 7. The rubber composition of claim 6, further comprising silica.
 8. A pneumatic tire comprising the rubber composition of claim
 7. 